To manufacture semiconductor devices, various heat treatment apparatuses are used to perform heat treatment on an object to be processed, for example, a semiconductor wafer. The heat treatment includes oxidation, diffusion, Chemical Vapor Deposition (CVD), and annealing. For example, a vertical heat treatment apparatus may perform heat treatment on a plurality of wafers at one time. The vertical heat treatment apparatus includes: a processing vessel made of quartz that has an opening at a lower portion thereof; a cover that opens/closes the opening of the processing vessel; a retention device that is disposed on the cover and retains a plurality of the objects to be processed at certain intervals in a vertical direction; a furnace body that is disposed around the processing vessel; and a heater which heats the objects to be processed in the processing vessel.
Conventionally, in order to control the temperature in the furnace body with a high precision, a space in the furnace body is segmented into a plurality of regions, an in-furnace temperature sensor is disposed in each of the plurality of regions, and the temperature in each of the segmented regions is separately and carefully controlled by a heater.
Here, a K thermocouple or an R thermocouple is used as the in-furnace temperature sensor. In this case, when a measured temperature of the furnace body is greatly changed, a Seebeck coefficient (represents a degree of generation of an electromotive force relative to a change in temperature) of the K thermocouple is changed. That is, an electromotive force from the K thermocouple is required to be calibrated when the measured temperature is changed.
Further, even if the Seebeck coefficient of the R thermocouple or S thermocouple need not be changed, using the R thermocouple or the S thermocouple is expensive, thereby increasing the cost of manufacturing.